SEAWEEDS OF THE BLACKWATER ESTUARY 317 Orton, J. H. and Lewis, H. M. (1930). The Effects of the Severe winter of 1928-29 on the Oyster Drill, with records of 5 years temperature observations in the Blackwater Estuary. J. Mar. biol. Ass., 17: 301-13. Parke, M. and Dixon, P. (1964). A revised check-list of British Marine algae. J. Mar. biol. Ass. U.K., 44: 499-542. Powell, H. T. (1963). Speciation in the genus Fucus L. and related genera. System. Ass. Publ., 5: 149-64. Prat, H. (1933). Les zones de vegetation et les facies des rivages de l'estuaire du St. Laurent, en voisinage de Trois-Pistoles. Le Nat. Canad., 60: 93-136. Rees, T. K. (1935). The Marine Algae of Lough Ine. J. Ecol., 23, 1 : 1-147. Soderstrom, J. (1963). Studies in Cladophora. Bot. Gothoburg. Spenser, J. F. (1963). Research Report No. 8/63. Internal Report, Central Electricity Generating Board, South-Eastern Region. Taylor, W. R. (1957). The Marine Algae of the North-Eastern Coast of North America. U. of Michigan. APPENDIX Systematic list of species recorded in essex Chlorophyceae Chlorococcales Characiaceae Characium marinum Kjellm. St. Peters Flats (River Blackwater). Epiphytic on Ceramium deslongchampsii. G.M.M., 1963. Endosphaeraceae Chlorochytrium facciolae (Borzi) Bristol. Canvey Island, Carter (1933). Chlorochytrium inclusum Kjellm. Harwich, Batters (1894). Ulotrichales Ulotrichaceae Ulothrix flacca (Dillw.) Thur. Felixstowe, Clacton, Southend, Batters (1894); Canvey Island, Carter (1933); River Blackwater (St. Peters Flats, Osea Island, Bradwell Creek), G.M.M., 1963-64. Ulothrix pseudoflacca Wille. Canvey Island, Carter (1933). Ulothrix subflaccida Wille. Canvey Island, Carter (1933). Monostromataceae Monostroma oxyspermum (Kutz.) Doty. Maldon, Batters (1894) (as M. laceratum Thur.). Ulvaceae Blidingia minima (Kutz.) Kylin. Clacton, Batters (1894); Canvey Island, Carter (1933); Osea Island (River Blackwater), G.M.M., 1963; (as Enteromorpha minima). Enteromorpha clathrata (Roth.) Grev. Wivenhoe, Maldon, Walton Ferry, Clacton, Batters (1894) (as E. erecta J. Ag.); River Blackwater (St. Peters Flats, Stone, Bradwell Creek), G.M.M., 1963.